1. 44th Rencontres de Moriond, 7th February 20081 Luísa Arruda on behalf of the GAW collaboration LIP – Laboratório de Instrumentação e Física Experimental de Partículas GAW A Very Large Field of View Imaging Atmospheric Čerenkov Telescope

2. Observing the High Energy Sky 2 44th Rencontres de Moriond, 7th February 2008 Milagro 10 9 10 11 101010 10 131517 19 1 GeV1 TeV1 PeV1 EeV Satellites Fly’s Eye / HiRes IACTs EAS Arrays Solar Arrays Akeno /Auger GAW

3. Scientific Motivation VHE gamma-ray astronomical events can occur at unknown locations and/or randomly in time. High sensitivity surveys of large sky regions are limited by the capability of the current observatories. 3 44th Rencontres de Moriond, 7th February 2008  Lower Energy Threshold (few tenths of GeV),  Improve Flux Sensitivity (in the entire VHE region),  Full sky coverage. The existing and planned ground-based observatories aim to fulfill three main objectives:

4. IACT Telescopes as CANGAROO III, HESS, MAGIC, VERITAS, … have  large collection area  reflective optics  high spatial resolution; excellent background rejection; which allow… wide energy range of  -rays: from tens of GeV to TeV; good sensitivity to sources; but …  survey of small sky areas;  low detection probability for serendipity transient sources or stables sources far from the galactic plane;  Small field of view (3º-5º) Shower particles arrays ARGO, Tibet-HD and Milagro very large FoV, more than one steradian large duty cycle  sensitivity is some order of magnitude worse than IACT and achieved with much longer exposure. 4 Current gamma-ray detection techniques 44th Rencontres de Moriond, 7th February 2008

5. FOV increase in IACTs: limitations 5 Whipple Veritas 44th Rencontres de Moriond, 7th February 2008 Large reflector mirrors (up to 17 m Ø) are used by the current IACTs. Field of View enlargement is compromised due to:  image degradation for off-axis imaging

6. FOV increase in IACTs: limitations 6 Whipple Veritas Large reflector mirrors (up to 17 m Ø) are used by the current IACTs. Field of View enlargement is compromised due to:  image degradation for off-axis imaging 44th Rencontres de Moriond, 7th February 2008 It is necessary to review the current geometry of the IACTs!  the shadow of the focal surface increase

7. Detector at the focal surface Mirror (reflective) Detector at the focal surface Lens (refractive) reflective refractive The GAW concept: Optics  GAW proposes the usage of refractive optics to increase the FOV and to avoid the camera shadow Novel technique using Fresnel lenses: a “refractive” Fresnel lens can work as an efficient light collector! small thickness good transmittance easy replication –> low cost solution! no shadow large FoV Requirements Requirements: Cromaticity should be controlled at level <0.1º

8.  Instead of the usual charge integration method, GAW front-end electronics design is based on single photoelectron counting mode. Keeps negligible the electronics noise and the PMT gain differences. Strongly reduces the minimum number of p.e. required to trigger the system. Requirement: pixel size small enough to minimize p.e. pile up within intervals shorter than sampling time (10ns). The MAPMT R7600-03-M64 chosen as baseline for GAW satisfies such a requirement. With current camera design is confortable with: Threshold of 14 p.e per sample per trigger-cell (2x2 MAPMT) Expected NSB contribution is 2-3 p.e. per sample per trigger-cell. 8 Charge Integration (Analog) Single Photon Counting (Digital) 1 TeV gamma triggered event pe pile up 1 pe 2 pe 3 pe The GAW concept: Focal Plane

9. 9 44th Rencontres de Moriond, 7th February 2008 GAW telescope design Each telescope is equipped with  a Fresnel lens  a focal surface detector formed by a grid of 10x10 MultiAnode pixelized (8x8) photoMultiplier Tubes coupled to light guides. GAW is a pathfinder gamma ray experiment, sensitive in the 1-10 TeV energy region. Colaboration between institutes in Italy (IASF, Palermo), Portugal (LIP, Lisbon) and Spain (CIEMAT, Granada, Sevilla). The R&D telescope is planned to be located at Calar Alto Observatory (Sierra de Los Filabres - Almeria Spain), at 2168 m a.s.l.

10. 213 cm Ø 50.8 cm Ø 40.6 cm 10 44th Rencontres de Moriond, 7th February 2008 GAW optics Baseline Optics Module for GAW prototype LensFlat single-sided Diameter2.13 m Focal Length2.56 m f/#1.2 Material UV Transmitting Acrylic Refraction Index 1.517 (at  = 350 nm) Standard Thickness3.2 mm Trasmittance~95% (330-600 nm, from UV to Near Infra Red) GAW uses a non-commercial Fresnel lens as light collector. Optimized for maximum of photon detection ( = 360 nm). central core + 12 petals + 20 petals + spider support will maintain all the pieces together.

11. 11 44th Rencontres de Moriond, 7th February 2008 GAW detection matrix: photomultipliers  MAPMT 8 × 8 (Hamamatsu R7600-03-M64)  UV sensitive [200,680] nm  Effective area 18.1 mm x 18.1 mm  Spatial granularity (  0.1º) suitable for Cherenkov imaging  Good quantum efficiency for > 300 nm (>20% @ 420 nm)  High gain ~ 3×10 5 for 0.8 kV voltage, low noise  Fast response (< 10 ns)

12. 12 44th Rencontres de Moriond, 7th February 2008 Detection matrix: light guides  ~55% of the photons would be lost without any guiding device  LG are made of 8x8 independent acrylic plastic tubes glued on a plastic plate  Tubes:  pyramidal polyhedron shaped  material: PMMA from Fresnel Technologies (n=1.4893)  Pieces hold together by 1mm layer on the top made of anti-reflective PMMA vs h LG for FOV [0-12]º PMMA Fresnel vs h LG for FOV [0-12]º  LG vs (X,Y) for  <32º h LG = 20 mm h LG = 25 mm 26.6 mm 1 mm h LG Gap = 0.5 mm h LG = 20-25 mm

13. GAW timeline 13 2005 - 2007 Telescope Design and site choice

14. GAW timeline 14 2005 - 2007 Telescope Design and site choice 2007 Project proposal approved (Phase 1 approved)

15. GAW timeline 15 2005 - 2007 Telescope Design and site choice 2008 - 2009 Construction and begin of installation Lens purchase: lens design and commissioning 2007 Project proposal approved (Phase 1 approved)

16. GAW timeline 16 2005 - 2007 Telescope Design and site choice 2008 - 2009 Construction and begin of installation Lens purchase: lens design and commissioning 2007 Project proposal approved (Phase 1 approved) 2010 Test full apparatus: 1 telescope 6°×6° FoV

17. GAW timeline 17 2005 - 2007 Telescope Design and site choice 2008 - 2009 Construction and begin of installation Lens purchase: lens design and comissioning 2007 Project proposal approved (Phase 1 approved) 2010 Test full apparatus: 1 telescope 6°×6° FoV 2011 Results on R&D Test bench for new technological solutions for the focal plane

18. Results on R&D Test bench for new technological solutions for the focal plane GAW timeline 18 2005 - 2007 Telescope Design and site choice 2008 - 2009 Construction and begin of installation Lens purchase: lens design and commissioning 2007 Project proposal approved (Phase I approved) 2010 Test full apparatus: 1 telescope 6°×6° FoV 2011 2012 Phase II 24°×24° FoV 80 m U2 - Pinta U3 – Sta Maria U1 - Niña

19. Conclusions 19 44th Rencontres de Moriond, 7th February 2008 IACT challanges for the next years: Improve sensitivity Lower the threshold for  rays detection Higher FOV GAW intends to proof that it is possible to combine both good sensitivity with large FOV. GAW will use: a Fresnel lens as a refractive light collector, single photoelectron counting mode as detection working method. 2011: Results proving the feasibility of the technique. Good test bench for IACTs improvement.

20. 20 44th Rencontres de Moriond, 7th February 2008 GAW project Phase 1 (2007-2011): testing - calibration phase GAW in testing configuration 6°×6° FoV Moving the detector along the FoV, the sensitivity of GAW will be tested observing the Crab Nebula on-axis and off-axis pointing up to 12°. GAW will also monitor the VHE activity of some flaring Blazars Phase 2 (>2011) GAW with Large Field of View 24°×24° FoV pointing along different North- South directions, GAW would reach a survey of 360°×60° sky region. Once the method has been successfully proved

21. 21 44th Rencontres de Moriond, 7th February 2008 Current status Housing for the telescope prototype already built at Calar Alto (Granada). Telescope mechanical structure built and in place. Fresnel lens purshage being negotiated. First tests with the prototype foreseen for the end of 2009.

22. 22 44th Rencontres de Moriond, 7th February 2008 GAW array 80 m U1 - Niña U2 - Pinta U3 – Sta Maria

23. 23 44th Rencontres de Moriond, 7th February 2008 GAW prospects: collecting area The collecting area is evaluated for mono- energetic  -ray events coming from an on-axis source (zenith angle=0°) and with a 3-Fold Telescopes trigger coincidence: the fiducial area (1520×1520 m 2 ) is multiplied by the ratio between the detected and generated events. GAW and the Crab Nebula. GAW collecting area has been convolved with a Crab-like spectrum. The figure shows the differential detection rate of the Crab Nebula vs energy, which peaks at 0.7 TeV.

24. 24 44th Rencontres de Moriond, 7th February 2008 GAW prospects: sensitivity GAW sensitivity with 6°×6° FoV. “Phase 1” 24°×24° FoV GAW sensitivity with 24°×24° FoV. “Phase 2” GAW/VERITAS GAW light collector (2.13 m Ø) / VERITAS (12 m Ø) GAW is competitive, mainly at higher energies, thanks to the gain of a factor more than 100 in the useful FoV -> GAW will observe the same sky region for longer exposure time in the same clock-time interval. The sensitivity limit is evaluated using a source with a Crab-like spectrum.